1. Field of the Invention
This invention relates to a stepping motor initialization control apparatus and, particularly, to an exhaust gas recirculation valve control apparatus wherein an exhaust gas recirculation valve disposed in an exhaust gas recirculation passage is driven by a stepping motor.
2. Description of Related Art
In exhaust gas recirculation apparatuses (so-called EGR apparatuses) such as shown in Japanese Patent Publication No. H.2-38783 (U.S. Pat. No. 4,391,244), there have been those which, by using a stepping motor as means for driving an exhaust gas recirculation valve (EGR valve) for controlling the amount of exhaust gas recirculated, are able to finely control the opening degree of the exhaust gas recirculation valve.
With these apparatuses, to make the rotational position of the stepping motor and the opening degree of the exhaust gas recirculation valve correspond correctly, before controlling the exhaust gas recirculation valve it is necessary to initialize the stepping motor and certainly set the rotational position of the stepping motor to the fully closed position (reference position) of the exhaust gas recirculation valve. For this reason, conventional exhaust gas recirculation apparatuses initialize the stepping motor immediately after the ignition switch is turned OFF; to perform this initialization a main relay control circuit is provided to keep a main power supply relay in an ON state for a predetermined period after the ignition switch is turned OFF so that current can be supplied to the stepping motor for a predetermined period after the ignition switch is turned OFF, and the stepping motor is initialized during this period.
However, with such conventional apparatuses as described above, because initialization (return to the fully closed position) of the stepping motor is carried out after turning the ignition switch OFF, if the stepping motor once steps out during exhaust gas recirculation control (hereinafter called `EGR control`), there is no occasion for the positional error due to the stepping out to be corrected (i.e. there is no occasion for initialization to be carried out) until the ignition switch is turned OFF, EGR control is continued with the stepping motor stepped out and there is a likelihood of this causing reduction in the engine output and deterioration of the drivability of the vehicle.